Processes are presently in commercial use which treat whey for the separation and production of various useful products, including whey protein products and lactose. One such process makes use of membrane ultrafiltration which serves to separate the whey into two fractions, one being a protein-rich fraction, and the other being a permeate rich in lactose. Such a process is disclosed in Canadian Pat. No. 966,361 dated Apr. 22, 1975. The composition of a typical whey permeate obtained by application of membrane ultrafiltration depends upon a number of factors, including the character and source of the whey, and the manner in which the membrane ultrafiltration is carried out. The principal constituents include lactose, mineral salts, protein, non-protein nitrogen (NPN), and a small amount of fat. The mineral salts include both the natural buffer salts of milk, and also mineral salts resulting from the cheese making process from which the whey is derived. A general composition range (dry solids basis) for permeate derived from acid and sweet wheys is as follows:
______________________________________ Lactose 68.0 to 87.0% Protein 3.0 to 5.5% NPN 0.4 to 0.8% Fat 0.1 to 0.2% Ash 8.5 to 14.0% Titratable acidity 2.0 to 14.0% ______________________________________
The term acid whey is used in the dairy industry to designate whey produced in the manufacture of cottage cheese. The term sweet whey refers to whey produced in the manufacture of other cheeses, such as Cheddar and mozzarella. Both acid and sweet wheys have a natural acidity as shown by the above general composition.
The high level of mineral salts tends to impart undesirable flavor characteristics. When processed for the removal of lactose by crystallization, which involves concentration of the permeate, certain of the salts precipitate out, together with crystallization of the lactose, and this tends to reduce the lactose yield and decrease its purity. While the permeates include substances of value, their disposal without processing poses a serious problem since it is an ecological pollutant.
Commercial processes for the manufacture of lactose generally remove lactose from whey concentrate by crystallization (see U.S. Pat. No. 2,439,612 dated Apr. 13, 1948). Such lactose is relatively impure, since it contains some whey protein and mineral salts. Resolution and recrystallization is employed to obtain products of higher purity. The remaining mother liquor is not suitable for human consumption and cannot be discarded to waste because of adverse ecological effects.